In a known injection nozzle, commonly referred to as a variable orifice nozzle (VON), a nozzle body is provided with a blind bore within which a first, outer valve is movable under the control of an actuator. The bore provided in the nozzle body defines a seating surface with which the outer valve is engageable to control fuel delivery through a first set of nozzle outlets provided at a first axial position along the length of the nozzle body. The outer valve is itself provided with a further bore within which a second, inner valve needle is able to move. The inner valve needle projects through the open end of the further bore in the outer valve and is engageable with the seating surface to control fuel delivery through a second set of outlets provided at a second, lower axial height along the length of the nozzle body.
The outer valve is operable either to move alone, so that the outer valve is lifted away from its seating but the inner valve needle remains seated, or so as to cause the inner valve needle to move also. Movement of the outer valve is transmitted to the inner valve needle, causing the inner valve needle to lift too, in circumstances in which the outer valve is moved through an amount exceeding a predetermined threshold amount. During this stage of operation, both the first and second sets of outlets are opened to give a relatively high fuel delivery rate. If the outer valve is lifted through an amount less than the predetermined threshold amount, the inner valve needle remains seated so that injection only occurs through the first set of outlets at a lower fuel delivery rate.
Variable orifice nozzles of the aforementioned type provide particular advantages for diesel engines, in that they provide the flexibility to inject fuel into the combustion chamber either through the first set of outlets on its own or through both the first and second outlets together. This enables selection of a larger total fuel delivery area for high engine power modes or a smaller total fuel delivery area for lower engine power modes.
A fuel injection nozzle of the aforementioned type is described in our co-pending European patent application EP 04250132.0 (Delphi Technologies Inc.).
It has now been recognised that the performance of existing variable orifice nozzles may be improved further by taking steps to improve the flow efficiency through the nozzle. It is with a view to addressing this issue that an improved injection nozzle is provided by the present invention. A more convenient method of manufacturing the injection nozzle is also provided.